Thousands of wildlife habitats, including refuges for some of the country's rarest species and sites recognised worldwide for their importance to nature are under threat from development every year.

The scale of the problem – from small garden-grabs to the construction of major housing estates, ports and roads – is revealed as the Guardian today launches a project called Piece by piece, to expose the creeping threat to Britain's natural world.

Jonathon Porritt, one of the UK's most influential environmental experts, said Piece by piece, a dedicated website that will collect evidence of developments and challenges to these , was "desperately" needed.

"If it's been badly needed over the last few years, I think that need is likely to become absolutely desperate over the next few years," said Porritt, former head of both Friends of the Earth and the government's Sustainable Development Commission.

"The [government] is intent on setting aside some of the restrictions and constraints in the current planning process in a way that will promote local decision-making at the expense of environmental safeguards. I think we're just going to slide back to pretty crude nimbyism."

Piece by piece has also been backed by leading conservation groups and has cross-party political support.

Hilary Benn, Labour shadow environment secretary, said: "Nature nurtures our souls and lifts our spirits. But it also sustains us and our economy – and it is for this reason that we take it for granted at our peril."

Caroline Spelman, the Conservative secretary of state for the environment, said: "Our natural environment needs help. Piecemeal degradation has eroded many gains made and reversing the decline of our biodiversity is one of my Department's main priorities."

Figures for the national threat posed by development to open spaces are hard to collect. But several campaign groups have provided the Guardian with information that illustrates the scale of the problem.

The Wildlife Trusts Federation, which has the most comprehensive overview, last year asked for 4,900 projects to be changed or stopped. These were the most damaging schemes it selected after reviewing 83,000 planning applications. Before the recession, those annual figures were higher, usually more than 5,000 objections from over 90,000 applications.

The Royal Society for the Protection of Birds, which concentrates on only the most nationally and internationally important sites for birds, was fighting 1,600 developments last year, including more than 700 added during 2009.

Focusing only on the remnants of Britain's centuries-old ancient woodland, dubbed "Britain's rainforests" for their rich mix of plants and animals, the Woodland Trust currently has 180 sites under threat from building projects. In the last decade it has fought to protect 800 sites comprising up to 100sq miles – an area the size of Birmingham.

Yesterday the government published figures showing one in seven new homes were being built on "residential" land – mostly gardens. Garden Organic, which has campaigned to protect these small patches of land that sustain wildlife in cities and provide vital corridors for species to reach the countryside, calculates that from 2006-2016, a quarter of a million gardens will be concreted and bricked over.

WWF, which campaigns more on wider issues than individual projects, said it is concerned about the indirect impacts of developments on biodiversity, for example when projects take water from local streams and rivers, or add to pollution problems.

In one case in the UK, the charity has demonstrated a direct link between building new homes and the drying-out of stretches of rare chalk streams, rich with trout, kingfishers and otters, which flowed regularly for centuries, with the exception of major droughts.